Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.87	12.605%	$147.3662	$147.37	$147.35	$147.40
Purchase #2	$164.32	10.841%	$182.1339	$182.13	$182.15	$182.10
Purchase #3	$85.89	5.232%	$90.3838	$90.38	$90.40	$90.40
Purchase #4	$79.27	8.354%	$85.8922	$85.89	$85.90	$85.90
Purchase #5	$72.88	3.687%	$75.5671	$75.57	$75.55	$75.60
Purchase #6	$33.30	4.348%	$34.7479	$34.75	$34.75	$34.70
Purchase #7	$46.48	6.814%	$49.6471	$49.65	$49.65	$49.60
7 purchase totals =	$613.01		$665.7382	$665.74	$665.75	$665.70